Tube protective circuit



A ril 18, 1950 E. c. KLUENDER TUBE PROTECTIVE CIRCUIT Filed April 2'7,1946 Fig. I.

Inventor. Edward C. Kluender,

DRIVER His Attorney.

Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE TUBE PROTECTIVECIRCUIT Edward C. Kluender, Schenectady, N. Y., assignor to GeneralElectric Co New York mpany, a corporation of Application April '27,1946, Serial No. 665,365

might resuit'i'rom a short or open circuit in the antenna or other loadconnected thereto causes. the radio frequency component of space path,

voltage greatly to decrease, thereby causing a greater average spacepath voltage during the conduction time of the device. The energy dissipated therein is accordingly increased and, un-

less steps are taken immediately to disconnect the Space path potentialsource, destruction of the device will result.

It is an obJect of this invention to prevent accidental overload ofelectron discharge devices in energy converting equipment.

5 Claims. (Cl. l79171) 5 1. In the figure, curve electrode voltageapplied to an electron discharge It is a further object of thisinvention to provide improved means to prevent overload of electrondischarge devices in energy converting equipment, which means does notinterfere with the normal functioning of the equipment for its intendedpurpose. while at the same time is capable of immediately interruptingoverloadgerous operating temperatures are approached.

Yet another object of this invention is to 'provide overload protectionfor an electron discharge device used in power conversion equipment in amanner simple of construction and reliable in operation and readilyapplicable to various types of power conversion equipment.

j The novel features characteristicof my inven-' tion are set forth withparticularity in the appended claims. My invention itself, however,

both as to its organization and method of opera--,v

tion may best be understood by reference to the following descriptiontaken in connection with the accompanying drawing in which Fig. 1 showsthereof or producing a suitable signal when danone method wherebyelectron discharge devices maybe overloaded and Fig. 2 shows an embodiment of my invention capable of preventing this overload.

" By way of illustration, the method by which" class Cradio frequencyoscillators and amplifiers mayjbe accidentally overloaded will first bedescribed with reference to Fig. 1. It will be understood, of course,that this invention is applicable to protection of electron dischargedevices used in power converting equipment generally and is not limitedto this particular application;

' device.

average value of space path voltage is no indica- 2 L A represents thecontroldevice operating in the class C condition. In this case thenegative unidirectional bias voltage 0Y maintains the control electrodevoltage E; below the cut-ofi bias OX except during ,a small portion ofthe positive portion of each cycle. The

corresponding cathode-anode space path voltage is shown in curve B. Thisvoltage consists of a sine wave voltage of radio frequency Ep superimposed on the unidirectional space path voltage OZ. The radio frequencycomponent of this voltage is 180 out of phase with the control electrodevoltage so that minimum cathode-anode voltage exists at the instant ofmaximum control electrode voltage.

control electrode voltage is less than the cut-off bias value and hasasharp peaked wave shape Ip when the bias is above cut-oil.

The energy dissipated within the electron dis-,- charge device isdetermined by the integrated product of instantaneous space current ilowand space path voltage. These two values under nor mal conditions ofoperation are shown in the cross It should be noted that neitherspacepath current flow nor space sectioned areas of' Fig. 1.

path voltage. drop of itself is a measure of this energy as a high valueof one of these factors;

accompanied by a lowyalue of the other, maynot involve any increase inenergy to be dissi-- pated. Hence neitherspace current flow nor spacepath voltage may be used to indicate the energy dissipated. within theelectron discharge It'should further be noted that the tion of theenergy dissipated within the electron discharge-device inasmuch as thespace currentflows only during a portion of the cycle, this por--- tioncorresponding to a period of minimum space path voltage. Hence, averagespace current flow cannot be combined with average space path voltage tomeasure the energy dissipated Within the electron discharge device. I

If maladjustment of the tuned circuits, a change in load impedance (suchas an antenna short circuit or open circuit), or other event reducesthe. alternating component of the space path voltage. across theelectron discharge device, the space. path voltage during the instantcurrent fiow occurs is increased as shown in the dashed curve labeledEp', Fig. 1. This increased space path voltage causes a correspondingincrease in space path current during the period of current flow asshown in curve 113'. These two efiects combine to cause an exaggeratedincrease in the energy, dissipated within the electron discharge deviceand, if the change is great, will quickly cause the r 9 e h a ca b eca eOften s Curve C shows the cathode-; anode space path current of theelectron discharge'device'. This current is zero so longas thean anode,a control electrode, and a, screen grid 7 the. value of'ithisvoitagfheingidterrninedibythe,

'tected in accordance with the princiiflesof this invention. In thefigure, anelectaton device is indicated at I having-aheaterhcarthpd agelectrode. Radio frequency control electrode voltage is applied to thisdevice 'fion'r drivers through coupling condenser 3. Unidirectional,control electrode bias is derived from voltage source 21 throughradidfrequency choke coil 25. The voltage of source 2"! is-' chosentojpil'odiice sufiicientnegative' potential atfthe control elec ti-ode" of devicei tocause" that'devi'oe" to" be biased: tocutoff excepteurm me aesnee nor: tioncf ther-adio *frequenc'y' controlelectfod 7volt?- age: curve; condensersbypasses radio? as; quency currents abon'tsource 21? Ca thode screen electrode spacepath voltage for device I issupplied from unidirectional voltage source through-relay-contactsTfCondenser ajbypassesf to-g round' anyradio freuuency voltage: appearingat the screen- Cathode-anode space, path voltage for device'1'isisuppliedirbhr unidirectien'a1- voltage'-sourcethroughf relaycontacts; and radio frequency choke-won If)"; Itisf "the. purpeseof thelatterdviceto prevent. source" F from bypassing radio frequency voltagesfrom; the anode to reunde 1 I The anode of dvice i is:coupledhy'tondenser II- toa utilization' circuitishown gerreralhiiat I2?, This circuit consists ofaresoriantfcircuithavifig a' load-suchas'a'radiatingjantenna cqupledjtditl For purposes of explanation; it Iisfshowr'r. as an.

' a'pproxi-rnateequivalent "circnificomprising corr l" denser'I3';inductance Iitj andjresistane :11 Undernormal=operatingconditions;theresonant frequency ofcondenser" 'I 3and inductahcefllfcor responds to"the frequency-of-*the"applied:cbntiolf. electrode-voltage and the-value "of resistance 15} issufiicie'ntly larg" to roduce-0mg aifinitederrect on thisfrequencyz" As 'expiainedapovefany maladjustment;short'circuitj or open circuitwilli cause device'- I 2"-to' heniistunedjthereby;- causing? a; decrease in the-impedance thereof: anfr'edil eingthe radio frequency 'vol'tagefatithe'anodeof 5:0

device I: This correspondingly?" increases the losses within thatdevicei I The protective circuit-flier device 1 "includes 7 re? lay I6and electrorr discharge dvice It is" the ur ose of theiattefdvicetc'fproducea 111112; direetio'nar voltage varying "iaccordahcwith" the alternating componenttofsp'ace patl'r"'voltage: ofdevice I. This' is' accomplishedfby" coupling? part of'thevoitageacross'utilitatiorfdeviceil23:6 device I'I. This couplihg'fis'provided" bY'thf' capacitive voltage "divid'r comprisih'g capacitors,

parallelcombinationpfresistancei2i'fandjcapaci the periodof theradiorrqueneywaves-across utilizationdeviceI 2': 'rhis,causes"a-"supstantiailyf constant voltagato appear aeross resistancefi Iradio frequencyyvoltagefacross: device I2; Th

r or device I from source 6.

. trodespace-current flowiirdevice I diic'edTby amplifying "the r A v pbefore applicationtode polarity of this "'voltage is such cause the 7 5cathode of device I! to become positive with respecttoground' potentfakaZ k r relay; shown generall""at24';"is' provided to disconnect the anodeand screen grid electrodes Current flow in coil L6 opens contacts 1 and8. Operating coil I6 is con'riectedbetween the cathode of device I andthe: cathode of device} I! so that the current flow therethroug-h;depends on the difierence between the relative voltage; at these points.'When this I difierence exceeds a predetermined value in eitherdirection; therelay operates, thereby opening contacts I and 8 todisconnect source 6 from the various electrodes of device I andpreventing further spacepath energy flow to device I. 7

when an -inerease--iriaverage foathdde afilide space current" flow-indevice I takes" place, the voltage d1"op-aci'ossresist 'nc'e" Wisaccordingly increasedi This vifltage'dfp is" substantially constant byreason-off the smoothing? actio'r'i' of capacitor -5 However, ir-pacorrespending; crease in radio frequency output'voltagtakeslplacey-the'voltageat the'cathodeofdevic ITwiil be raised; thereby pev-landmine increa's" rent "flow in operatingf coil" IS that would therwise be associated" the in cre edspace cur: ism-flow;l-lcwevenif'irodh'cr in graditifrefquency output voltage" takesier 1; epotential. of the catho d-e ofd'evice ITwillreinainfcohstantfa'ndthe'-greater-catho dejvolfiagei device I- Willi r V overload isimnrirrentwlfile permitting lloadYin;

creases that do not involve such overload? It will be notedthati'twcathdd sereen e e resistance 4 and influencesperformaneeofrehyzfl accordinglyr Actuallyi 'thi's eurren't'is' sb small compared to thecathocfe-arro pace'path cuff rentthat thee'ffec'ts "so 'produfcetiareliot 'signifi cant'inscfar as-rel ayfi is concernedi If;throu'gir-sorne changes-Entrie-amplifiererr: cii'itiardbadFth'eradicrfiequency outputvoitage' of device'l' is decreasedithe potent i ofdevic'e I Ms-cqrre nd V, p w p v chane'is' accompani V I y i ction inspace current flow ofsufficient "magnitude? to "prevent Voverheatingoffdvice I3 a; c m'sponamg redue tion inthe-cathodepotentialfofthe latter? device-f will time place and n iner'easedf current new Onthe other hand; i thej spa c'e'current fiow ifi device il is-notreduced? the vortageiatth'e 'cath- I ode or device FWiH" remaifithe"'sarne' j and" relay 2E will" operate, thereby preventing? the'ftube?damage that-would"0therwisbe 'associatedwith; this condition: j V e V fp 7 In" general; 1 prefer to: chooseresistance" 4 to:

I have the smallest:resiStancepbssibIe tirerebyre ducingfj 'the power;los'sassocia rdfw'ith thefpresjence ofthisf resistanf'ceiin the 'space"path u'rr'ent-fj path ofdevic'e I. Thispowerlossms Wel impedanceefiects, associated with, condenstje 8;' I9; 256; and "22", reslsta,cesiiif an df'23jj and "device l'liimay be even furtherrreddeediby'actuatingyr' lay 24f'from a separateErriplififpioiiidd.for [thejpurpose; Furthermore, the. effects. offthe coiitrbll circuit;acrossiutilizatiofi device; ITniayfbf rd': requencyybltageg If desired,tiine'fidelity apparatus iri'aybe'prm' vided in connection with relay 24even further to improve the performance of the circuit. In this case,the time delay is made to correspond with the thermal time constants ofthe elements of device I so that the relay operates only after a timedelay determined by the ability of device I to stand short timeoverloads.

If desired, relay 24 may be a single pole relay connected only tointerrupt the supply of screen electrode potential to device I, chokecoil Ill being directly connected to the positive terminal of source 6.In this case, device I will be protected from overload by loss of screenelectrode voltage, an event sufficient to avoid overheating in mostcases. Alternatively, relay 24 may be connected to actuate an alarmdevice, such as a bell or light, thereby to warn the operator of theequipment and enable him to take appropriate steps to prevent damage. Itwill, of course, be apparent to those skilled in the art that operationof relay 24 may be made to cause these events as well as many otherswithout departing from the true spirit and scope of this invention.

The term energy converting equipment or energy conversion system as usedherein refers to equipment wherein an electron discharge device is usedas a means of converting energy of one type, as for example,unidirectional voltage, to another type, as for example alternatingvoltage, and characterized by the fact that the power dissipated in theelectron discharge device is determined by the difference between theapplied energy of one type and the output energy of another type.

While I have shown and described my invention as applied to a particu arsystem of connections and embodying various devices diagrammaticallyshown. it will be obvious to those ski led in the art that changes andmodifications may be made without departing therefrom. In particular,the methods described herein may be used to protect electron dischargedevices in circuits other than the class C radio frequency amplifiershown, such other circuits including, for example. class C oscillators,class A oscillators and amplifiers, and class B oscillators andamplifiers. I therefore aim in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthis invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a high frequency electron discharge amp ifier havingan output circuit coupled for energy transfer at said high frequency toa load impedance, means to derive a first unidirectional potentialproportional to the peak voltage at said frequency developed across saidimpedance. means to derive a second unidirectional potentialproportional to the average space current in said amplifier, relay meansactuated by said potentials when the difference between them exceeds apredetermined value, and means controlled by actuation of said relay tolimit said space current to a safe value.

2. In combination, an electron discharge amplifier having input andoutput circuits, means for supplying oscillations to said input circuit,a resonant load device coupled to said output circuit and tuned to thefrequency of said oscillations, peak voltage rectifying means suppliedwith oscillations from said load device for developing a firstunidirectional voltage, resistance means common to said input and outputcircuits and shunted by a low capacity at said frequency for developinga second unidirectional voltage, and

relay means responsive to said voltages for removing operating potentialfrom said amplifier when the difference between said voltages exceeds apredetermined value.

3. In an energy conversion system, an electron discharge device havingan anode-cathode space path, means to impress anode operating potentialon said device, a utilization device, means to supply power from saidspace path to said utilization device, means to produce a firstunidirectional voltage which is a function of the current in said spacepath, means to produce a second unidirectional voltage which is afunction of the voltage appearing across said utilization device, arelay having an operating coil, means for impressing said voltages onsaid coil in opposing polarity, said relay being arranged to be actuatedonly when the difference between said voltages exceeds a predeterminedvalue, and means controlled by actuation of said relay to limit saidcurrent to a safe value.

4.. In an energy conversion system, an electron discharge device havinga cathode, a control electrode and an anode, means to apply oscillationsto said control electrode, means to impress anode-cathode operatingpotential on said device, a utilization device, said last deviceincluding a resonant circuit normally tuned to the frequency ofoscillations from said first means, means connecting said utilizationdevice to said discharge device, means to produce a first unidirectionalvoltage proportional to the average value of space current fiow in saiddischarge device, rectifying means energized from said resonant circuitto produce a second unidirectional voltage proportional to the voltageacross said circuit, a relay, means for impressing said voltages on saidrelay in opposite polarity, said relay being arranged to be actuated bysaid voltages only when the difference between them exceeds apredetermined value, and means controlled by actuation of said relay tolimit said space current to a safe value.

5. In combination, an electron discharge device having a cathode, anauxiliary electrode, and an anode, means to impress anode-cathodeoperating potential on said device, means to impress operating potentialon said auxiliary electrode, a utilization device, means to cause saiddischarge device to supply converted energy to said utilization device,means to produce a first unidirectional voltage proportional to theconverted energy supplied to said utilization device, means to produce asecond unidirectional voltage proportional to the average value ofanode-cathode space current flow in said discharge device, and meansresponsive to the difference between said voltages to disconnect saidsecond means from said auxiliary electrode when said difference exceedsa predetermined value, thereby to limit said space current.

EDWARD C. KLUENDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

